ci: add retry logic for Go module operations (#21609)

## Description

Add exponential backoff retries to all `go install` and `go mod
download` commands across CI workflows and actions.

## Why

Fixes
[coder/internal#1276](https://github.com/coder/internal/issues/1276) -
CI fails when `sum.golang.org` returns 500 errors during Go module
verification. This is an infrastructure-level flake that can't be
controlled.

## Changes

- Created `.github/scripts/retry.sh` - reusable retry helper with
exponential backoff (2s, 4s, 8s delays, max 3 attempts), using
`scripts/lib.sh` helpers
- Wrapped all `go install` and `go mod download` commands with retry in:
  - `.github/actions/setup-go/action.yaml`
  - `.github/actions/setup-sqlc/action.yaml`
  - `.github/actions/setup-go-tools/action.yaml`
  - `.github/workflows/ci.yaml`
  - `.github/workflows/release.yaml`
  - `.github/workflows/security.yaml`
- Added GNU tools setup (bash 4+, GNU getopt, make 4+) for macOS in
`test-go-pg` job, since `retry.sh` uses `lib.sh` which requires these
tools

.github/workflows/release.yaml

@@ -121,7 +121,7 @@ jobs:
       - name: Build dylibs
         run: |
           set -euxo pipefail
-          go mod download
+          ./.github/scripts/retry.sh -- go mod download
 
           make gen/mark-fresh
           make build/coder-dylib
@@ -259,7 +259,7 @@ jobs:
           java-version: "11.0"
 
       - name: Install go-winres
-        run: go install github.com/tc-hib/go-winres@d743268d7ea168077ddd443c4240562d4f5e8c3e # v0.3.3
+        run: ./.github/scripts/retry.sh -- go install github.com/tc-hib/go-winres@d743268d7ea168077ddd443c4240562d4f5e8c3e # v0.3.3
 
       - name: Install nsis and zstd
         run: sudo apt-get install -y nsis zstd
@@ -341,7 +341,7 @@ jobs:
       - name: Build binaries
         run: |
           set -euo pipefail
-          go mod download
+          ./.github/scripts/retry.sh -- go mod download
 
           version="$(./scripts/version.sh)"
           make gen/mark-fresh